/usr/share/pyshared/zfec/filefec.py is in python-zfec 1.4.5-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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from pyutil import fileutil
from pyutil.mathutil import pad_size, log_ceil
import array, os, struct
CHUNKSIZE = 4096
from base64 import b32encode
def ab(x): # debuggery
if len(x) >= 3:
return "%s:%s" % (len(x), b32encode(x[-3:]),)
elif len(x) == 2:
return "%s:%s" % (len(x), b32encode(x[-2:]),)
elif len(x) == 1:
return "%s:%s" % (len(x), b32encode(x[-1:]),)
elif len(x) == 0:
return "%s:%s" % (len(x), "--empty--",)
class InsufficientShareFilesError(zfec.Error):
def __init__(self, k, kb, *args, **kwargs):
zfec.Error.__init__(self, *args, **kwargs)
self.k = k
self.kb = kb
def __repr__(self):
return "Insufficient share files -- %d share files are required to recover this file, but only %d were given" % (self.k, self.kb,)
def __str__(self):
return self.__repr__()
class CorruptedShareFilesError(zfec.Error):
pass
def _build_header(m, k, pad, sh):
"""
@param m: the total number of shares; 1 <= m <= 256
@param k: the number of shares required to reconstruct; 1 <= k <= m
@param pad: the number of bytes of padding added to the file before encoding; 0 <= pad < k
@param sh: the shnum of this share; 0 <= k < m
@return: a compressed string encoding m, k, pad, and sh
"""
assert m >= 1
assert m <= 2**8
assert k >= 1
assert k <= m
assert pad >= 0
assert pad < k
assert sh >= 0
assert sh < m
bitsused = 0
val = 0
val |= (m - 1)
bitsused += 8 # the first 8 bits always encode m
kbits = log_ceil(m, 2) # num bits needed to store all possible values of k
val <<= kbits
bitsused += kbits
val |= (k - 1)
padbits = log_ceil(k, 2) # num bits needed to store all possible values of pad
val <<= padbits
bitsused += padbits
val |= pad
shnumbits = log_ceil(m, 2) # num bits needed to store all possible values of shnum
val <<= shnumbits
bitsused += shnumbits
val |= sh
assert bitsused >= 8, bitsused
assert bitsused <= 32, bitsused
if bitsused <= 16:
val <<= (16-bitsused)
cs = struct.pack('>H', val)
assert cs[:-2] == '\x00' * (len(cs)-2)
return cs[-2:]
if bitsused <= 24:
val <<= (24-bitsused)
cs = struct.pack('>I', val)
assert cs[:-3] == '\x00' * (len(cs)-3)
return cs[-3:]
else:
val <<= (32-bitsused)
cs = struct.pack('>I', val)
assert cs[:-4] == '\x00' * (len(cs)-4)
return cs[-4:]
def MASK(bits):
return (1<<bits)-1
def _parse_header(inf):
"""
@param inf: an object which I can call read(1) on to get another byte
@return: tuple of (m, k, pad, sh,); side-effect: the first one to four
bytes of inf will be read
"""
# The first 8 bits always encode m.
ch = inf.read(1)
if not ch:
raise CorruptedShareFilesError("Share files were corrupted -- share file %r didn't have a complete metadata header at the front. Perhaps the file was truncated." % (inf.name,))
byte = ord(ch)
m = byte + 1
# The next few bits encode k.
kbits = log_ceil(m, 2) # num bits needed to store all possible values of k
b2_bits_left = 8-kbits
kbitmask = MASK(kbits) << b2_bits_left
ch = inf.read(1)
if not ch:
raise CorruptedShareFilesError("Share files were corrupted -- share file %r didn't have a complete metadata header at the front. Perhaps the file was truncated." % (inf.name,))
byte = ord(ch)
k = ((byte & kbitmask) >> b2_bits_left) + 1
shbits = log_ceil(m, 2) # num bits needed to store all possible values of shnum
padbits = log_ceil(k, 2) # num bits needed to store all possible values of pad
val = byte & (~kbitmask)
needed_padbits = padbits - b2_bits_left
if needed_padbits > 0:
ch = inf.read(1)
if not ch:
raise CorruptedShareFilesError("Share files were corrupted -- share file %r didn't have a complete metadata header at the front. Perhaps the file was truncated." % (inf.name,))
byte = struct.unpack(">B", ch)[0]
val <<= 8
val |= byte
needed_padbits -= 8
assert needed_padbits <= 0
extrabits = -needed_padbits
pad = val >> extrabits
val &= MASK(extrabits)
needed_shbits = shbits - extrabits
if needed_shbits > 0:
ch = inf.read(1)
if not ch:
raise CorruptedShareFilesError("Share files were corrupted -- share file %r didn't have a complete metadata header at the front. Perhaps the file was truncated." % (inf.name,))
byte = struct.unpack(">B", ch)[0]
val <<= 8
val |= byte
needed_shbits -= 8
assert needed_shbits <= 0
gotshbits = -needed_shbits
sh = val >> gotshbits
return (m, k, pad, sh,)
FORMAT_FORMAT = "%%s.%%0%dd_%%0%dd%%s"
RE_FORMAT = "%s.[0-9]+_[0-9]+%s"
def encode_to_files(inf, fsize, dirname, prefix, k, m, suffix=".fec", overwrite=False, verbose=False):
"""
Encode inf, writing the shares to specially named, newly created files.
@param fsize: calling read() on inf must yield fsize bytes of data and
then raise an EOFError
@param dirname: the name of the directory into which the sharefiles will
be written
"""
mlen = len(str(m))
format = FORMAT_FORMAT % (mlen, mlen,)
padbytes = pad_size(fsize, k)
fns = []
fs = []
try:
for shnum in range(m):
hdr = _build_header(m, k, padbytes, shnum)
fn = os.path.join(dirname, format % (prefix, shnum, m, suffix,))
if verbose:
print "Creating share file %r..." % (fn,)
if overwrite:
f = open(fn, "wb")
else:
flags = os.O_WRONLY|os.O_CREAT|os.O_EXCL | (hasattr(os, 'O_BINARY') and os.O_BINARY)
fd = os.open(fn, flags)
f = os.fdopen(fd, "wb")
f.write(hdr)
fs.append(f)
fns.append(fn)
sumlen = [0]
def cb(blocks, length):
assert len(blocks) == len(fs)
oldsumlen = sumlen[0]
sumlen[0] += length
if verbose:
if int((float(oldsumlen) / fsize) * 10) != int((float(sumlen[0]) / fsize) * 10):
print str(int((float(sumlen[0]) / fsize) * 10) * 10) + "% ...",
if sumlen[0] > fsize:
raise IOError("Wrong file size -- possibly the size of the file changed during encoding. Original size: %d, observed size at least: %s" % (fsize, sumlen[0],))
for i in range(len(blocks)):
data = blocks[i]
fs[i].write(data)
length -= len(data)
encode_file_stringy_easyfec(inf, cb, k, m, chunksize=4096)
except EnvironmentError, le:
print "Cannot complete because of exception: "
print le
print "Cleaning up..."
# clean up
while fs:
f = fs.pop()
f.close() ; del f
fn = fns.pop()
if verbose:
print "Cleaning up: trying to remove %r..." % (fn,)
fileutil.remove_if_possible(fn)
return 1
if verbose:
print
print "Done!"
return 0
# Note: if you really prefer base-2 and you change this code, then please
# denote 2^20 as "MiB" instead of "MB" in order to avoid ambiguity. See:
# http://en.wikipedia.org/wiki/Megabyte
# Thanks.
MILLION_BYTES=10**6
def decode_from_files(outf, infiles, verbose=False):
"""
Decode from the first k files in infiles, writing the results to outf.
"""
assert len(infiles) >= 2
infs = []
shnums = []
m = None
k = None
padlen = None
byteswritten = 0
for f in infiles:
(nm, nk, npadlen, shnum,) = _parse_header(f)
if not (m is None or m == nm):
raise CorruptedShareFilesError("Share files were corrupted -- share file %r said that m was %s but another share file previously said that m was %s" % (f.name, nm, m,))
m = nm
if not (k is None or k == nk):
raise CorruptedShareFilesError("Share files were corrupted -- share file %r said that k was %s but another share file previously said that k was %s" % (f.name, nk, k,))
if k > len(infiles):
raise InsufficientShareFilesError(k, len(infiles))
k = nk
if not (padlen is None or padlen == npadlen):
raise CorruptedShareFilesError("Share files were corrupted -- share file %r said that pad length was %s but another share file previously said that pad length was %s" % (f.name, npadlen, padlen,))
padlen = npadlen
infs.append(f)
shnums.append(shnum)
if len(infs) == k:
break
dec = easyfec.Decoder(k, m)
while True:
chunks = [ inf.read(CHUNKSIZE) for inf in infs ]
if [ch for ch in chunks if len(ch) != len(chunks[-1])]:
raise CorruptedShareFilesError("Share files were corrupted -- all share files are required to be the same length, but they weren't.")
if len(chunks[-1]) == CHUNKSIZE:
# Then this was a full read, so we're still in the sharefiles.
resultdata = dec.decode(chunks, shnums, padlen=0)
outf.write(resultdata)
byteswritten += len(resultdata)
if verbose:
if ((byteswritten - len(resultdata)) / (10*MILLION_BYTES)) != (byteswritten / (10*MILLION_BYTES)):
print str(byteswritten / MILLION_BYTES) + " MB ...",
else:
# Then this was a short read, so we've reached the end of the sharefiles.
resultdata = dec.decode(chunks, shnums, padlen)
outf.write(resultdata)
return # Done.
if verbose:
print
print "Done!"
def encode_file(inf, cb, k, m, chunksize=4096):
"""
Read in the contents of inf, encode, and call cb with the results.
First, k "input blocks" will be read from inf, each input block being of
size chunksize. Then these k blocks will be encoded into m "result
blocks". Then cb will be invoked, passing a list of the m result blocks
as its first argument, and the length of the encoded data as its second
argument. (The length of the encoded data is always equal to k*chunksize,
until the last iteration, when the end of the file has been reached and
less than k*chunksize bytes could be read from the file.) This procedure
is iterated until the end of the file is reached, in which case the space
of the input blocks that is unused is filled with zeroes before encoding.
Note that the sequence passed in calls to cb() contains mutable array
objects in its first k elements whose contents will be overwritten when
the next segment is read from the input file. Therefore the
implementation of cb() has to either be finished with those first k arrays
before returning, or if it wants to keep the contents of those arrays for
subsequent use after it has returned then it must make a copy of them to
keep.
@param inf the file object from which to read the data
@param cb the callback to be invoked with the results
@param k the number of shares required to reconstruct the file
@param m the total number of shares created
@param chunksize how much data to read from inf for each of the k input
blocks
"""
enc = zfec.Encoder(k, m)
l = tuple([ array.array('c') for i in range(k) ])
indatasize = k*chunksize # will be reset to shorter upon EOF
eof = False
ZEROES=array.array('c', ['\x00'])*chunksize
while not eof:
# This loop body executes once per segment.
i = 0
while (i<len(l)):
# This loop body executes once per chunk.
a = l[i]
del a[:]
try:
a.fromfile(inf, chunksize)
i += 1
except EOFError:
eof = True
indatasize = i*chunksize + len(a)
# padding
a.fromstring("\x00" * (chunksize-len(a)))
i += 1
while (i<len(l)):
a = l[i]
a[:] = ZEROES
i += 1
res = enc.encode(l)
cb(res, indatasize)
try:
from hashlib import sha1
except ImportError:
# hashlib was added in Python 2.5.0.
import sha as sha1
def encode_file_not_really(inf, cb, k, m, chunksize=4096):
enc = zfec.Encoder(k, m)
l = tuple([ array.array('c') for i in range(k) ])
indatasize = k*chunksize # will be reset to shorter upon EOF
eof = False
ZEROES=array.array('c', ['\x00'])*chunksize
while not eof:
# This loop body executes once per segment.
i = 0
while (i<len(l)):
# This loop body executes once per chunk.
a = l[i]
del a[:]
try:
a.fromfile(inf, chunksize)
i += 1
except EOFError:
eof = True
indatasize = i*chunksize + len(a)
# padding
a.fromstring("\x00" * (chunksize-len(a)))
i += 1
while (i<len(l)):
a = l[i]
a[:] = ZEROES
i += 1
# res = enc.encode(l)
cb(None, None)
def encode_file_not_really_and_hash(inf, cb, k, m, chunksize=4096):
hasher = sha1.new()
enc = zfec.Encoder(k, m)
l = tuple([ array.array('c') for i in range(k) ])
indatasize = k*chunksize # will be reset to shorter upon EOF
eof = False
ZEROES=array.array('c', ['\x00'])*chunksize
while not eof:
# This loop body executes once per segment.
i = 0
while (i<len(l)):
# This loop body executes once per chunk.
a = l[i]
del a[:]
try:
a.fromfile(inf, chunksize)
i += 1
except EOFError:
eof = True
indatasize = i*chunksize + len(a)
# padding
a.fromstring("\x00" * (chunksize-len(a)))
i += 1
while (i<len(l)):
a = l[i]
a[:] = ZEROES
i += 1
# res = enc.encode(l)
for thing in l:
hasher.update(thing)
cb(None, None)
def encode_file_stringy(inf, cb, k, m, chunksize=4096):
"""
Read in the contents of inf, encode, and call cb with the results.
First, k "input blocks" will be read from inf, each input block being of
size chunksize. Then these k blocks will be encoded into m "result
blocks". Then cb will be invoked, passing a list of the m result blocks
as its first argument, and the length of the encoded data as its second
argument. (The length of the encoded data is always equal to k*chunksize,
until the last iteration, when the end of the file has been reached and
less than k*chunksize bytes could be read from the file.) This procedure
is iterated until the end of the file is reached, in which case the part
of the input shares that is unused is filled with zeroes before encoding.
@param inf the file object from which to read the data
@param cb the callback to be invoked with the results
@param k the number of shares required to reconstruct the file
@param m the total number of shares created
@param chunksize how much data to read from inf for each of the k input
blocks
"""
enc = zfec.Encoder(k, m)
indatasize = k*chunksize # will be reset to shorter upon EOF
while indatasize == k*chunksize:
# This loop body executes once per segment.
i = 0
l = []
ZEROES = '\x00'*chunksize
while i<k:
# This loop body executes once per chunk.
i += 1
l.append(inf.read(chunksize))
if len(l[-1]) < chunksize:
indatasize = i*chunksize + len(l[-1])
# padding
l[-1] = l[-1] + "\x00" * (chunksize-len(l[-1]))
while i<k:
l.append(ZEROES)
i += 1
res = enc.encode(l)
cb(res, indatasize)
def encode_file_stringy_easyfec(inf, cb, k, m, chunksize=4096):
"""
Read in the contents of inf, encode, and call cb with the results.
First, chunksize*k bytes will be read from inf, then encoded into m
"result blocks". Then cb will be invoked, passing a list of the m result
blocks as its first argument, and the length of the encoded data as its
second argument. (The length of the encoded data is always equal to
k*chunksize, until the last iteration, when the end of the file has been
reached and less than k*chunksize bytes could be read from the file.)
This procedure is iterated until the end of the file is reached, in which
case the space of the input that is unused is filled with zeroes before
encoding.
@param inf the file object from which to read the data
@param cb the callback to be invoked with the results
@param k the number of shares required to reconstruct the file
@param m the total number of shares created
@param chunksize how much data to read from inf for each of the k input
blocks
"""
enc = easyfec.Encoder(k, m)
readsize = k*chunksize
indata = inf.read(readsize)
while indata:
res = enc.encode(indata)
cb(res, len(indata))
indata = inf.read(readsize)
# zfec -- fast forward error correction library with Python interface
#
# Copyright (C) 2007 Allmydata, Inc.
# Author: Zooko Wilcox-O'Hearn
#
# This file is part of zfec.
#
# See README.txt for licensing information.
|